The invention relates to a device for measuring the particle emissions of an internal combustion engine, in particular for measuring the concentration of soot in the exhaust gas. Between a transmitter and a receiver, the device has a signal transmission route that traverses a flow of exhaust gas delivered to an exhaust gas tube.
Such devices are used in engines having fuel injection pumps. From the engine particle emissions, these devices derive a control variable for the fuel injection, with which variable the injection quantity at full load can be metered such that the maximum specified particle emission will not be exceeded (U.S. Pat. No. 3,744,461).
In a known device of this kind (British Pat. No. 1,334,472), an electrical detector is installed at the circumference of the exhaust tube carrying exhaust gas, and it receives a signal from an electrical transmitter that is also disposed on the circumference of the exhaust tube, directly opposite the detector. The intensity of the signal received by the detector--increases or decreases--depending on the type of detector whenever the concentration of soot in the flow of exhaust gas increases. The electrical output signal of the detector is amplified and forms a direct control signal for adjusting a valve. To preclude errors in measurement, caused by soot concentration at the detector and transmitter, as much as possible, a scavenging air curtain is disposed between the exhaust gas, on the one hand, and the active elements of the detector and transmitter, on the other. Nevertheless, deposits of soot on the active elements are unavoidable, if there is a long-term drift in the measured value.